The vast majority of excitatory synapses occur on spines, which are dynamic structures that undergo changes in size, shape, and number during development and in response to physiological stimuli such as neuronal activity and learning. The overall goal of this research project is to elucidate the molecular mechanisms that regulate dendritic spine morphogenesis. Spine development includes formation, maturation, and pruning. Although many proteins have been found to be important for spine formation, the molecular pathway controlling spine formation is not fully understood. Even less is known about the molecular mechanism regulating the later phases of spine development, especially spine pruning, which is an activity-dependent process and likely plays an important role in the refinement of synaptic connections. The gene for brain-derived neurotrophic factor (BDNF) produces two pools of mRNA, with either a short or long 3' untranslated region (3'UTR). Our recent findings show that short 3'UTR Bdnf mRNA is restricted to the soma, whereas long 3'UTR Bdnf mRNA is also transported to dendrites for local translation. This application is aimed at testing the hypothesis that BDNF synthesized in the soma and dendrites regulates formation, maturation, and pruning of spines via distinct signaling cascades and that single nucleotide polymorphisms (SNP) in the human Bdnf 3'UTR may impair localization and translation of Bdnf mRNA in dendrites, leading to spine dysmorphogenesis and cognitive impairments. These hypotheses will be tested in three specific aims. Specific aim 1 proposes to examine the distinct roles of somatically and dendritically synthesized BDNF in spine morphogenesis in cultured rat hippocampal neurons. Specific aim 2 proposes to elucidate the signaling cascades mediating the effects of BDNF on the formation, maturation, and pruning of spines. Specific aim 3 proposes to determine the effects of a human SNP in the long Bdnf 3'UTR on spine morphogenesis and synaptic plasticity. Findings from these studies likely reveal novel mechanisms governing gene function and spine morphogenesis, and provide insights into the functional consequence of SNPs in non-coding sequences.